In previously developed monohull sailing vessels, heeling forces from the sail plan are counteracted by the use of a fixed keel, the movement of the crew, movement of water or other ballast, or lately the utilization of swinging keels in the which the ballasted keel is mechanically swung towards the windward side of the vessel, or any combination of the above features.
The use of the swinging ballasted keel has provided the most benefit in terms of extracting more speed from sailing vessels of all sizes, but has resulted in a system that requires significant power input from either crew or stored power systems to operate. It also has the major drawback that any failure of the mechanical controlling devices or keel itself can and has resulted in totally uncontrolled movement of the ballasted keel and the subsequent destruction of the keel support area of the hull with disastrous and terminal damage that can and has resulted in the foundering of the vessel.
Many sailing vessels are known in the art that adopt some sort of hydrofoil system for improving stability and/or performance of the sailing vessel. Generally such hydrofoils are utilized in multi-hull designs and in some cases, monohull designs, with the intention of fully supporting the displacement of the vessel and lifting the vessel fully out of the water by dynamic forces only.
A hydrofoil, or more simply, a foil, is a streamline body designed to give lift and is similar to aircraft wings. The foil generally has a different curvature or camber at opposed surfaces. The static angle of attack (AoA) of a foil is the angle between the chord, defined as the straight line connecting the leading and trailing edge of the foil, and the direction of movement of the boat. Foils are designed to have a controllable AoA to achieve the desired lifting forces in various types of water and at various boat speeds, loads, wind conditions, etc. Many types of adjustment mechanisms are known for adjusting and controlling the AoA. However, such devices are complicated, prone to failure, require constant adjustment, require a highly knowledgeable operator, are costly, and add weight.
Another manner of controlling the lifting force produced by the hydrofoil is to adjust the projected area and/or span of the hydrofoil. By exposing more of the hydrofoil to the passing water, greater lift can be achieved. However, like controlling the AoA, controlling the projected area of the hydrofoil results in a system that is complicated, prone to failure, requires constant adjustment, requires a highly knowledgeable operator, is expensive, and adds weight.
Further, it has been found that previously developed hydrofoils used on monohull sailing vessels use hydrofoils that have aspect ratios (the ratio of the foils length, i.e. wingspan, relative to its width) that are less than 2:1. These low aspect ratio foils have been found to be inefficient in terms of lift to drag ratios and have been found to have insufficient span to provide a significant increase to the total righting moment. Thus the total beneficial effects have not been sufficient to overcome the inherent additional drag and their development has been abandoned. In addition, the fore and aft location of these foils has been such that they would significantly increase the total drag of the vessel and thus not result in any performance increases and again this has discouraged further progress along this line.
Accordingly, there exists a need for a hydrofoil system for a monohull sailing vessel that is less complicated, reliable, requires less frequent adjustments, may be operated with little instruction, is relatively inexpensive, and is light weight.